请教关于字符串的，不知道怎么修改？

使用循环嵌套进行串搜索操作。不使用indexof方法
public class StringTest {
    public int j,i;
    public  boolean isSubString(String s,String t)
    {
        for(i=0;i<=t.length();i++)
            for( j=0;j<=s.length();j++)
               
            {
                if(s.charAt(j) != t.charAt(i))
                    break;
                else
                {
                    i++;
                    if(j==s.length())
                        return true;
                    continue;
                }
               
            }
   
            return false;
        
        
    }
    public static void main(String[] args) {
      StringTest aaa=new StringTest();
        if(aaa.isSubString("hat", "The cat in the hat"))
            System.out.print("true");
        else
            System.out.print("false");
        
    }

}

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for(i=0;i<t.length();i++){
    int mark = i;
    for(j=0;j<s.length();){
        if(t.charAt(mark++)!=s.charAt(j++)
              break;
        }
    if(mark==s.length())
        return ture;
    return false;
}

----------------解决方案--------------------------------------------------------
谢了
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